CN101603819B - Real-time measurement method for wood deformation microstructure characteristics - Google Patents

Abstract

The invention discloses a method for real-time measurement of wood deformation microstructure features, comprising the following steps: 1) loading the wood to be detected; 2) enlarging the area to be tested through a microscopic unit during the loading process; 3) collecting images through an image acquisition unit After information, the image processing unit calculates the X-axis length X ₀ ~X _n and the Y-axis length Y ₀ ~Y _n of each cell on the loading surface at each image acquisition moment; 4) According to the X-axis length of each cell before deformation Length X ₀ and Y-axis length Y ₀ , and X-axis length X _n and Y-axis length Y _n after cell deformation calculate the compressive or tensile strain ε _xn and ε _yn of a single cell on the X-axis and Y-axis, ε _xn =( X _n -X ₀ )/X _n , ε _yn =(Y _n -Y ₀ )/Y _n ; 5) Compression and tension of all individual cells on the X-axis and Y-axis in the area to be tested enlarged by the microscopic unit The strains ε _xn and ε _yn are averaged to obtain the compressive and tensile strains ε _x and ε _y of the overall wood on the X-axis and Y-axis. The invention can measure micro-area tissue and cell strain, realize micro-area deformation quantification, and monitor micro-area defects.

Description

A real-time measurement method for wood deformation microstructure characteristics

technical field

The invention relates to a real-time measurement method for mechanical strength properties such as compression or tension and deformation microstructure characteristics of wood and wood composite materials. the

Background technique

In the process of production, processing and use of wood and wood composite materials, it is inevitable to encounter mechanical behaviors such as compression or tension. The detection of mechanical properties of materials is the key to ensuring the quality of subsequent products and their rational use. The performance and microstructural effects of materials or products, as well as the influence of microstructural features on the overall performance of materials, are still unclear. the

For the current detection methods, the single macroscopic mechanical property detection is the main one. This detection method has many defects and shortcomings:

1. Judging the performance of wood materials only by macroscopic mechanical behavior is insufficient to grasp the performance of the material itself;

2. Only the result of the mechanical behavior of the material can be understood, but the cause of the mechanical behavior is not known;

3. The testing process cannot take into account the temperature, moisture content and other influencing factors of the tested material;

4. The strain obtained during the detection process is the average strain of the material as a whole, which does not reflect the strain of different organizational structures of the material; it cannot reflect the relationship between the structure of each part of the wood and the overall stress and strain;

5. For an anisotropic heterogeneous material such as wood, the obtained strain results are single, which cannot truly reflect the stress-strain results of each tissue structure of wood;

6. After the test is over, the springback of the tested material cannot be obtained in time, and the residual stress of the tested material cannot be analyzed. the

Contents of the invention

The technical problem to be solved by the present invention is to provide a real-time measurement method for wood deformation microstructure characteristics, which can measure the microstructure characteristics and mechanical properties of material deformation online in real time. the

In order to solve the above problems, the invention provides a real-time measurement method for wood deformation microstructure characteristics, comprising the following steps:

1) Load the material to be tested;

2) Magnify the area to be tested through the microscopic unit during the loading process;

3) After the image information is collected by the image acquisition unit, the X-axis length X ₀ to X _n and the Y-axis length Y ₀ to Y _n of each cell on the loading surface at each image acquisition moment are calculated by the image processing unit as the loading process The deformation data of the tested material;

4) According to the X-axis length X ₀ and Y-axis length Y ₀ of each cell before deformation, and the X-axis length X _n and Y-axis length _{Y n} after cell deformation, calculate the compression or tension of a single cell on the X-axis and Y-axis Strain ε _xn and ε _yn , ε _xn =(X _n -X ₀ )/X _n , ε _yn =(Y _n -Y ₀ )/Y _n , (n=1, 2, 3...N );

5) The compressive or tensile strains ε _xn and ε _yn of all individual cells in the area to be tested enlarged by the microscopic unit on the X-axis and Y-axis are averaged to obtain ε _x and ε _y , which represent the measured material in the X-axis and the overall compressive or tensile strain on the Y axis,

Preferably, in the calculation of the image processing unit, the following steps are also included:

3.1) Calculate the tissue ratio A _i (i=0, 1, 2, ..., I) of various types of solid cell walls on the loading surface at each image acquisition moment, as the deformation of the measured material during the loading process data;

4.1) Calculate the overall strain ε _A of the measured material according to the tissue ratio A ₀ before cell deformation and the tissue ratio A _i after deformation, ε _A =(A _i -A ₀ )/A _i .

Preferably, after the mechanical behaviors such as stretching or compression end, the following steps are also included:

5) The measured material is continuously photographed by the image acquisition unit until the deformation and rebound of the measured material completely stops;

6) The image processing unit calculates the overall thickness or length L _k at any moment after the material under test is compressed or tensioned, thereby calculating the rebound amount R and the rebound rate R _r , R=L _k -L ₀ , R _r (%)=(L _k −L ₀ )×100/L ₀ ; where, k=0, 1, 2, . . . , K, “0” represents the moment just after the test.

Preferably, the temperature of the material to be tested is controlled within a certain range during the measurement process. the

Preferably, the moisture content of the material to be tested is controlled within a certain range during the measurement process. the

Preferably, said loading includes: tension, compression, bending, torsion or shear. the

The present invention has the following advantages:

1. The present invention combines the continuous mechanical testing process with the dynamic structural changes of wood, and can reflect the relationship between the mechanical properties of wood or wood composite materials and the changes in microstructure characteristics in real time. the

2. The present invention fully synchronizes the mechanical loading process, material performance data results, microstructure change images and time data points, and can establish a two-dimensional relationship between any two, and achieves real real-time "monitoring" and "measurement" ". the

3. The present invention can measure the tissue and cell strain of the micro-area, realize the quantification of the deformation of the micro-area, and monitor the defects of the micro-area. the

4. The present invention can test the relationship between the mechanical properties and microstructure changes of wood or wood composite materials, and can quantify the deformation and springback of materials after the mechanical loading process. the

5. The present invention extends the dynamic mechanical test to the range of low temperature or high temperature, and can establish the relationship between temperature and mechanical properties and microstructure changes. the

6. The present invention extends the dynamic mechanical test to the scope of water content change, and can establish the relationship between water content, mechanical properties and microstructure changes. the

7. The present invention adopts an automatic focusing system, which can effectively improve the image acquisition precision and shorten the image acquisition interval. the

8. The present invention can realize fully automatic computer operation, avoiding errors easily caused by manual control and separate control of each system. the

9. The stress-strain curve and micro-scale deformation mechanism obtained by the present invention can grasp the key to the ductility and strength of wood materials and wood composite materials. the

10. The present invention has a wide range of applications, and the range of mechanical loading loads such as compression or tension is wide, and it is suitable for

Samples of all types/shapes and sizes are studied, including solid wood materials, wood composites, other wood derived products, etc. the

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is a schematic diagram of the tested material of the present invention. the

Detailed ways

As shown in FIG. 1 , the present invention includes: a loading unit 1 , a temperature control box 3 , a sensor 4 , a computer 5 (ie, an image processing unit), an optical microscope 6 , a digital camera 7 and a video camera 8 . The loading unit 1 is used to perform mechanical behaviors such as compression, tension, or bending, shearing, and torsion of the tested material 2 . The temperature control box 3 is connected with the tension and compression unit 1 and the computer 5, and is used to control the temperature of the wood to be inspected (theoretical range -140～600°C). The optical microscope 6 is connected with a digital camera 7, a video camera 8 and a computer 5, and is used for collecting deformation images of the surface of the material under pressure or tension. 3 sets of sensors 4, one set is connected with the footage system 12 in the loading unit 1, and is used to measure the overall displacement of the measured material 2; one set is connected with the load control (pressure control or tension control, etc.) system 13, and measures the load value ( pressure or pulling force, etc.); one set is connected to the heat-conducting component (such as heat-conducting pressing block or stretching clip, etc.) 11, and is used for the temperature control box to control the temperature of the measured material 2. Both the digital camera 7 and the video camera 8 are connected with the computer 5 for data collection of stress and deformation images. The computer 5 is used to receive the detection data and image data of the footage system 12, the mechanical control system 13, the digital camera 7 and the video camera 8, and obtain the strain information and the rebound amount of the measured material through software calculation according to the displacement data results, and at the same time Get the stress-strain curve and real-time microstructure change results of the tested material. the

As shown in Figure 1, the optical microscope 6 can be an ordinary light trinocular biological microscope, which is composed of a spotlight illumination system 61, an eyepiece 62, an objective lens 63, an object stage 64 and a focusing mechanism, and is connected with a digital camera 7 and a video camera 8 , used for the acquisition of images of deformation of the stressed wood surface; wherein, the focusing mechanism is an autofocus system 65, which is arranged on the optical microscope, and one end is connected to the computer 5, which is used to control the focus adjustment of the optical microscope objective lens 63, and the adjustment is controlled by the computer 5 focus interval. the

As shown in Figure 1, the loading unit 1 is composed of a heat conducting component 11, a footage system 12, a load control system 13, and a cooling system 14, and is used for mechanical behaviors such as compression, stretching or bending of the wood 2 to be checked; wherein the cooling system 14 It is divided into two sets of water cooling and nitrogen cooling. Water cooling is used for cooling the heat conducting part 11 and the load control system 13 in the loading unit from high temperature to room temperature, and nitrogen cooling is used for cooling the heat conducting part 11 in the loading unit from room temperature to low temperature, thereby controlling The temperature of the material being measured. the

Since the present invention adopts the autofocus system 65 to automatically adjust the focal length of the objective lens 63 of the optical microscope 6 in real time, it can effectively improve the image acquisition precision and shorten the image acquisition interval. In addition, because the present invention adopts the camera 8, it is possible to observe in real time changes in the overall thickness or length of the material under test, such as external dimensions, so that the computer 5 connected to it can calculate the rebound of the material under test at any time after the force is applied. volume and rebound rate. In the present invention, a conventional auto-focus method may be used for auto-focusing. the

The specific measurement steps are as follows, as shown in Figure 1:

1) First measure the radial dimension L _R , the chord dimension L _T , and the longitudinal dimension L _L (as shown in Figure 2 ) of the tested material 2, and input them into the computer 5 as the original data of the tested material;

2) Place the measured material 2 on the loading unit 1, and set parameters such as maximum force (compression or tension, etc.) load, maximum compression ratio (or stretch ratio, deflection), loading speed, etc. in the computer 5;

3) Select an objective lens 63 with a suitable multiple on the optical microscope 6, and adjust to a reasonable focal length with an autofocus system 65, so that the images on the surface of the measured material 2 in the digital camera 7 and video camera 8 are clear and complete; set in the computer 5 The digital camera takes pictures at intervals, such as 5sec, 10sec, etc.; at the same time, set the auto-focus time interval of the auto-focus system 65, which is the same as that set by the digital camera, to ensure that the auto-focus is completed before each photo is taken;

4) If the temperature of the tested material 2 needs to be raised or lowered, first set the final temperature of the tested material in the computer 5, and turn on the switch of the temperature control box 3 ten minutes before the start of the measurement (the shortest time), so that the tested material 2 can gradually Heating (or cooling) to the set temperature;

5) start loading unit 1, digital camera 7, video camera 8, autofocus system 65 at the same time, and start testing;

6) The computer 5 controls the load control system 13 through the sensor 4 to obtain the size of the real-time loading load δ; obtain the real-time displacement data of the measured material through the footage system 12, and the computer 5 calculates the real-time strain ε _B of the measured material; through the digital camera 7 And video camera 8 obtains the clear real-time deformation image of tested material surface; The above data are sent to computer 5 in real time until the end of the test;

7) After the test is over, quickly remove the material to be tested from the loading unit 1, place it flat on the stage of the optical microscope and align it with the center of the objective lens, and continue to use the camera 8 to continuously shoot all the materials to be tested after the end of the stress. Days later, the image taken by the camera 8 is input into the computer 5 in real time;

8) According to the image data returned by the digital camera 7, the computer 5 calculates the real-time X-axis strain ε _x , Y-axis strain ε _y , and overall strain ε _A of the measured material by using two methods of calculating strain from the image, and calculates them Compared with the real-time strain ε _B calculated by the displacement data obtained by the footage system 12;

9) The computer 5 calculates the thickness (or length) L _k of the measured material at any moment after being stressed according to the image data sent back by the camera 8, and uses the formula to calculate the pressure (or tension) of the measured material at any time The rebound amount R at a moment, R=L _k -L ₀ , and the rebound rate R _r , R _r (%)=L _k -L ₀ )×100/L ₀ ; where, k=0, 1, 2 ,..., K, "0" represents the moment when the test just ended.

Through the above measurement steps, the stress-strain curve of the material during the entire loading process can be obtained, and the mechanical properties of the material in compression (or tension, etc.) can be obtained, such as elastic deformation stage, plastic deformation stage, yield point, and failure stage. , and the corresponding deformation images of the material microstructure. the

In the above-mentioned measurement steps, the loading unit 1, the temperature control box 3, the digital camera 7, the video camera 8, and the autofocus system 65 are all controlled and run synchronously by the computer 5, and the data obtained by each mechanism are also transmitted back to the computer 5 in real time. Like this, The load, temperature, strain and image data obtained by the above mechanisms can all establish a two-dimensional relationship with time as a reference. the

In addition, in the above measurement process, the moisture content of the material 2 to be tested can also be controlled within a certain range, thereby extending the dynamic mechanical test to the range of moisture content changes, and establishing the relationship between moisture content and mechanical properties and microstructure changes. relation. the

In addition, the present invention includes three methods of measuring strain, ① using a differential sensor to measure the average deformation to calculate the average strain ε _B , ② measuring the X-axis deformation and Y-axis deformation of each component unit (cells in wood) through images , and then calculate the overall X-axis and Y-axis average strain ε _x , ε _y of the measured material, ③ measure the change of the tissue ratio of the solid part of the unit (the solid part in wood is the cell wall) through the image, so as to calculate the measured The method for the overall average strain ε _A of the material. The data obtained by the three methods can be compared and complemented.

In summary, the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention. the

Claims (6)

1. a real-time measurement method for wood deformation microstructure features, characterized in that, comprising the steps: 1) Load the material to be tested; 2) Enlarge the area to be tested through the microscopic unit during the loading process; 3) After the image information is collected by the image acquisition unit, the X-axis length X ₀ to X _n and the Y-axis length Y ₀ to Y _n of each cell on the loading surface at each image acquisition moment are calculated by the image processing unit as a mechanical test Deformation data of the measured material during the process; 4) According to the X-axis length X ₀ and Y-axis length Y ₀ of each individual cell before deformation, and the X-axis length X _n and Y-axis length Y _n after cell deformation, calculate the compression or pressure of a single cell on the X-axis and Y-axis Tensile strain ε _xn and ε _yn , ε _xn ＝(X _n -X ₀ )/X _n , ε _yn ＝(Y _n -Y ₀ )/Y _n , (n=1, 2, 3... N); 5) The compressive or tensile strains ε _xn and ε _yn of all single cells in the X-axis and Y-axis in the area to be tested, which are enlarged by the microscopic unit, are averaged to obtain ε _x and ε _y , which represent the measured material in the X-axis and the overall compressive or tensile strain on the Y axis, ${\mathrm{\ϵ}}_x=\frac{\underset{N}{\overset{1}{\mathrm{\Σ}}}{\mathrm{\ϵ}}_{\mathrm{xn}}}{N}(\mathrm{no}=\mathrm{1,2},...,N),{\mathrm{\ϵ}}_{\mathrm{the\; y}}=\frac{\underset{N}{\overset{1}{\mathrm{\Σ}}}{\mathrm{\ϵ}}_{\mathrm{yn}}}{N}(\mathrm{no}=\mathrm{1,2},...,N).$ 2. The method according to claim 1, characterized in that, in the calculation of the image processing unit, further comprising the steps of: 3.1) Calculate the tissue ratio A _i (i=0, 1, 2, .., I) of various types of solid cell walls on the loading surface at each image acquisition moment, as the deformation data of the measured material during the loading process ; 4.1) Calculate the overall strain ε A of the measured material according to the tissue ratio A ₀ before cell deformation and the tissue ratio A _i after deformation, _{ε A =} (A _i -A ₀ )/A _i . 3. The method according to claim 1 or 2, characterized in that, after the loading ends, further comprising the steps of: 6) Continuously photographing the measured material through the image acquisition unit until the deformation and rebound of the measured material completely stops; 7) The image processing unit calculates the overall thickness or length L _k at any moment after the measured material is stressed, thereby calculating the rebound amount R and the rebound rate R _r , R=L _k −L ₀ , R _r (% )=(L _k −L ₀ )×100/L ₀ ; where, k=0, 1, 2, . . . , K, “0” represents the moment when the test just ended. 4. The method according to claim 3, characterized in that, the temperature of the measured material is controlled within a certain range during the measurement. 5. The method according to claim 4, characterized in that, the moisture content of the measured material is controlled within a certain range during the measurement process. 6. The method of claim 5, wherein the loading comprises: tension, compression, bending, torsion or shear.

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